1. Field of the Invention
This invention relates to an electromagnet system having an electromagnetic coil, wherein the wire windings of the exciting coil are supported by a coil form and are insulated from a magnetic flux element made of a ferromagnetically conductive material using a circuit element as a protection against overheating in the exciting circuit.
2. Description of Related Art
Preventive measures against overheating are part of the general state of the art. Thus, such preventive measures against overheating are also used for the exciting windings of electric motors and electromagnets. Either thermal circuit breakers or thermal fuses may be used. Thermal circuit breakers only interrupt power in the case of temperatures exceeding a predetermined limiting value, whereas thermal fuses cause a permanent interruption of the exciting circuit because of destruction resulting from overheating.
In electromagentic exciting coils, the use of such preventive measures is particulary important if such coils are only designed for short-term loads and there is a risk that long-term loads might occur. In this connection, during long-term loads, overheating of the exciting coil would result in the destruction of the wire insulation and, thus, in short-circuits. Therefore, preventive measures against overheating, be it in the form of a thermal circuit breaker or a thermal fuse, are integrated into the exciting coil. The threshold response value for the fuse element is selected to ensure that the critical temperature that would lead to the destruction of the exciting coil is not reached.
If the electromagnetic coil is subjected to such a load that the critical temperatures for the thermal fuse and, thus, the critical temperature for the electromagnet system is not reached, but high temperatures below these limiting values are generated on a relatively continuous basis, the area surrounding the electromagnetic coil, notably the magnetic flux element made of a ferromagnetically conductive material, is heated to high temperatures by the electromagnetic coil. In particular, when this element is placed in a plastic housing, it may lead to undesirable side effects, e.g., scorching. To avoid this, it may be necessary to take preventive measures against overheating in this area also. Based on this knowledge and the state of the art, the object of the invention is to provide an electromagnet system with protection against overheating to ensure in a simple manner that overheating both in the exciting coil and in the area surrounding it is prevented. In this connection, particular attention should be paid to the desire for a simple system and for making it available at a low cost.